1. Field of the Invention
The present invention relates to an organic light emitting display, and more particularly, to an organic light emitting display in which IR drop (i.e., voltage drop) in a cathode electrode is prevented or reduced.
2. Description of the Related Art
Recently, various flat panel displays (FPDs) that are light and thin in comparison to cathode ray tubes (CRTs) have been developed. Among the FPDs, organic light emitting displays using organic compound as phosphor to have excellent brightness and color purity are in the spotlight.
Since the organic light emitting displays are thin and light and capable of being driven with low power consumption, they are suitable for portable displays in addition to applications in larger size FPDs.
The organic light emitting displays are typically classified as a top emission organic light emitting display or a bottom emission organic light emitting display according to light emission directions. Further, a dual-side emission organic light emitting display has combined features of the top emission organic light emitting display and the bottom emission organic light emitting display.
A conventional bottom emission organic light emitting display has disadvantages of a low aperture ratio because thin film transistors for driving OLEDs cannot be positioned at light emitting regions.
On the contrary, the top emission organic light emitting display can achieve a desired aperture ratio regardless of whether or not the thin film transistors are located under the OLEDs.
However, in the top emission organic light emitting display, as light generated from an emission layer of the OLED is emitted out through a cathode electrode, the cathode electrode is required to be transparent. Therefore, the cathode electrode is made of a transparent conductive material such as ITO, or MgAg having a sufficiently small thickness to be transparent.
However, the transparent conductive material such as ITO has a high resistance, and MgAg can only have a limited thickness. Thus, resistance of the cathode electrode is high so that a relatively high IR drop (i.e., voltage drop) occurs. Particularly, as a display panel becomes larger in size, IR drop in the cathode electrode is greatly increased so that image quality and display characteristics may not be uniform.